Solid-state imaging elements (image sensors) using semiconductors are mounted on many apparatuses such as digital cameras, video cameras, monitoring cameras, copy machines, and facsimiles.
In recent years, so-called complementary metal oxide semiconductor (CMOS) solid-state imaging elements manufactured in addition to peripheral circuits in CMOS processes and have been considerably used as solid-state imaging elements. In the CMOS solid-state imaging elements, for example, photodiodes (PDs) converting received light into electric signals and floating diffusions (FDs) temporarily storing charges and sensing signals are formed using PN junctions of semiconductors.
On the other hand, in PN junctions, it is known that leak currents occur particularly when depletion layer regions formed in junction portions come into contact with surfaces or interfaces. In solid-state imaging elements, such leak currents are called dark currents. In order to improve image quality, it is necessary to reduce the leak currents as much as possible. As methods of reducing leak currents in PN junctions, methods of forming films having fixed charge in PN junction portions have been reported (see Patent Literatures 1 and 2).
Incidentally, in the related art, PDs in pixels of solid-state imaging elements are formed in semiconductor substrates. In semiconductor substrates, however, elements performing driving are also formed. Therefore, when sizes of pixels are reduced, it is difficult to take the areas of PDs. In order to take countermeasures, forming photoelectric conversion films serving as PDs outside of semiconductor substrates has been proposed (see Non-Patent Literatures 1 and 2).